A Service-Level Agreement (SLA) is a contract between the provider of packet network services and one of its customers (i.e., subscribers) that specifies some minimum quality of service that must be met or exceeded in the handling of calls identified with an application or service. One measure of performance that an SLA may specify is the amount of bandwidth that must be available on demand. A Virtual Private Network (VPN) is defined when the SLA specifies the amount of bandwidth that is to be made available, on demand, in each of a set of streams identified with the customer. A “stream” in this context is a node pair a of the network consisting of a source node and a destination node with respect to calls, in association with a particular class of service s. The various possible service classes may include, e.g., voice, data, e-mail, file tranfers, web browsing, and video. A packet network is, for example, a network supporting the ATM, IP, or Frame Relay protocol.
We will use the term “call” to denote any communicative transaction, or distinct subdivision of a communicative transaction, commonly referred to as a call, connection, or flow.
In the operation of a packet network, incoming calls identified with various customers must compete for the same network resources, such as link bandwidth capacity. Additionally, there is contention for the same resources by calls of different service classes, whether belonging to the same customer or to different customers. In such an environment, it is difficult to consistently provide each customer with the service quality it demands in each class of service, while also profitably operating the network.
One approach to this problem is to design the bandwidth loads Xsr of the network to accommodate the expected traffic patterns in an optimal way. Here, the design load Xsr is the designed bandwidth to be carried on a service route (s, r), i.e., on a route r between a given source-destination pair in a given service class s. A design method that explicitly recognizes the statistical properties of communication traffic is described, e.g., in U.S. Pat. No. 5,854,903 issued to D. Mitra et al. on Dec. 29, 1998 under the title “Optimization Method for Routing and Logical Network Design in Multi-Service Networks” and commonly assigned herewith. An extension of that exemplary design method to virtual private networks is described in the co-pending U.S. patent application Ser. No. 09/065,506, filed on Apr. 24, 1998 by D. Mitra et al. under the title “Method for Resource Allocation and Routing in Multi-Service Virtual Private Networks” and commonly assigned herewith. A design method based on concepts relating to multicommodity flow is described in U.S. patent application Ser. No. 09/370,826, filed on Aug. 9, 1999 by D. Mitra et al. under the title “Multicommodity Flow Method For Designing Traffic Distribution On A Multiple-Service Packetized Network” and commonly assigned herewith.
Although such off-line methods of network design are useful, they do not, by themselves, provide the ability to respond to traffic behavior in real time. However, because of the randomly fluctuating nature of traffic, there are often potential gains in total carried traffic or total revenue that could be realized if routing decisions could be informed by real-time measurements.